Multiple arc generated rotors having diagonally directed fluid discharge flow



Jan. 26, 1 960 J. E. WHITFIELD 1 MULTIPLE ARC GENERATED ROTORS HAVINGDIAGONALLY DIRECTED FLUID DISCHARGE FLOW Filed Sept. 26, 1957 16Shqets-Sheet 1 IN V EN TOR. Jasspfif. WHITFIELD A Tram/E Y Jan. 26, 1960E. WHITFIELD 2 922,377

J. MULTIPLE ARC GENERATED ROTORS HAVING DIAGONALLY DIRECTED FLUIDDISCHARGE FLOW Filed Sept. 26, 1957 16 Sheets-Sheet 2 IN V EN TOR.JbSEP/l E. Wmrnzw ATTOR/VE 7 Jan. 26, 1960 J. E. WHITFIELD 2,922,377 LLYMULTIPLE ARC GENERATED 'ROTORS HAVING DIAGONA DIRECTED FLUID DISCHARGEFLOW l6 Sheets-Sheet 3 Filed Sept. 26, 1957 Jase/w WHITFIELD BY rrar/VEYJan. 26, 1960 MULTIPLE ARC GENERA Filed Sept. 26, 1957 J E. WHITFIELD2,922,377

TED ROTORS HAVING DIAGONALLY DIRECTED FLUID DISCHARGE FLOW 16Sheets-Sheet 4 INVENTOR. JOSEPH tZM/rF/aa BY %W A TT'OEIVEY Jan. 26,1960 E .rEV[\ lH|T LD 2,922,377

MULTIPLE ARC G 'RA ROT ING DIAGONALLY DIRECTED FLUID DISCHA FLOW FiledSept. 26, 1957 16 Sheets-Sheet 5 /6. /Z I I 56. INVENTOR.

' ATl'dlF/VEY Jan. 26, 1960 J. E. WHITFIELD 2,922,377

MULTIPLE ARC GENERATED ROTORS HAVING DIAGONALLY DIRECTED FLUID DISCHARGEFLOW Filed Sept. 26, 1957 16 Sheets-Sheet 6 IN VEN TOR. Jaszmr E.WWW-762D Bi l/W Jan. 26, 1960 J. E. WHITFIELD 2,922,377

MULTIPLE ARC GENERATED ROTORS HAVING DIAGONALLY DIRECTED FLUID DISCHARGEFLOW Filed Sept. 26, 1957 16 Sheets-Sheet '7 IN V EN TOR. Joszm E.MwrF/ao rray/v 7 Jan. '26, 1960 J. E. WHITFIELD 2,922,377 MULTIPLE ARCGENERATED ROTORS HAVING DIAGONALLY DIRECTED FLUID DISCHARGE FLOW 16Sheets-Sheet 8 Filed Sept. 26, 1957 1 N VE N TOR. Josspn f. WHITFIELDrron A! E Y J. E. WHITFIELD 2,922,377 GENERATED ROTORS HAVING DIAGONALLYCTED FLUID DISCHARGE FLOW Jan. 26, 1960 MULTIPLE ARC DIRE l6Sheets-Sheet 9 Filed Sept. 26, 1957 INVENTOR.

d'bszP/l f. WHITFIELD BY jW Jan, 26, 1960 J. E. WHITFIELD 2,922,377

MULTIPLE A ENERATED ROTORS HAVING DIAGONALLY F m u Jan. 26, 1960 J. E.WHITFIELD 2,922,377

MULTIPLE ARC GENERATED ROTORS HAVING DIAGONALLY DIRECTED FLUID DISCHARGEFLOW 7 l6 Sheets-Sheet 11 Filed Sept. 26, 1957 km Q I IN V EN T 'OR.JOSEPH f; Mar/40 rrow/vs Y Jan. 26, 1960 J E H 922,377

2, MULTIPLE ARC GENERA ROT HAVING DIAGONALLY DIRECTED FLUID DISCHARGEFLOW Filed Sept. 26, 1957 16 Sheets-Sheet 12 IN V EN TOR.

Jose-1% f. Wynne-w ,4 TrdE/VS Y Jan. 26, 1960 J. E. WHITFIELD 2,922,377

MULTIPLE ARC GENERATED ROTORS HAVING DIAGONALLY DIRECTED FLUID DISCHARGEFLOW Filed Sept. 26, 1957 16 Sheets-Sheet 13 IN VEN TOR.

Jossm f. W/l/[f/ELD;

lay/W- ATIOKNEY Jan. 26, 1960 J. E. WHITFIELD 2,922,377

MULTIPLE ARC GENERATED ROTORS HAVING DIAGONALLY DIRECTED FLUID DISCHARGEFLOW Filed Sept. 26, 1957 16 Sheets-Sheet l4 Fla. 77

IN V EN TOR.

Jose/=11 t. mwrmsm BY ATT'dK NE Y 1960 J. E. WHITFIELD 2,922,377

MULTIPLE ARC GENERATED ROTORS HAVING DIAGONALLY DIRECTED FLUID DISCHARGEFLOW Filed Sept. 26, 1957 16 Sheets-Sheet 15 INVENTOR. Jasim f. Wl/THELDATTORNEY Jan. 26, 1960 WHIT LD 2,922,377

J. E. MULTIPLE ARC GENERATED ROT HAVING DIAGONALLY RGE FLOW DIRECTEDFLUID DISCHA Filed Sept. 26, .1957 16 Sheets-Sheet 16 FIG. 88 INVENTOR.

JOSEPH .fmy/rr/zw BY/%%W A rramvks Y United States Patent MULTIPLE ARCGENERATED ROTORS HAVING DIAGONALLY DRECTED FLUID DISCHARGE FLOW JosephE. Whitfield, York, Pa. Application September 26, 1957, Serial No.686,353

12 Claims. (Cl. 103-128) This invention relates generally to fluidpumps, motors, compressors, blowers, meters and similar devices in whichinterengaging rotary members are provided with helical intermeshingthreads and, more particularly, to the novel features of the rotarymembers, the housing in which they operate and other associated partsembodied with any one of these devices.

Screw-type fluid motors, blowers and the like have two or more helicallythreaded members rotatably supported with their axes parallel, forexample, and with their complementary threads intermeshing to provide acontinuous seal line the full length of the rotors. The housing enclosesboth of the rotary members and the perimetric tip of each thread forms aseal therewith. Thus any flow of fluid from one end of the members mustpass through the spaces enclosed by the threads on the rotary members incooperation with the housing.

The threads must be complementary to form satisfactory seals and spacesand permit rotation of the members. Thus one rotary member hasright-hand threads while the mating rotary member has left-hand threads.

While more than two rotary members can be used, only two will be shownand described herein for purposes of simplicity. The threads on one ofthe rotors usually lie wholly outside the pitch circle and do most ofthe work of compression; this rotor is termed the main rotor. Thethreads on the other rotor usually lie wholly within the pitch circleand forma Valve or gate across the path of the main rotor; this rotor istermed a gate rotor. Also the main rotor is sometimes called the malerotor and the gate rotor is sometimes called the female rotor but it ispreferred to designate them as main and gate rotors.

When rotated, the main rotor threads, in effect, act as a continuousseries of pistons which slide endwise through the troughs between thethreads of the gate rotor and produce a continuous series ofpockets-which convey the fluid from the suction end of the rotors to thedischarge end. The opening in the intake end of the housing is termedthe suction port and the opening in the outlet end is termed thedischarge port. Axial. flow screw-type devices of this generalconstruction are usually reversible, and such reversing reverses theports, but this description discloses a device that is more eflicientwhen operated in one certain direction and, in general, is notreversible.

This general type of device is old and well known in the art and is inuse for various purposes. However, heretofore, all such devices have hadcertain, very serious limitations. For instance, certain thread forms donot produce continuous seals between the rotors and leakage results.Others have low capacity for a given bulk size, while still others havea rotor form in which the threads on one member are not rigid enough forthe purpose, and several known thread forms are very diflicult tomachine accurately. However, the most serious fault with former rotordesigns is their formation of sealed pockets at the discharge end whichcreate excessive pressure, temperature and noise. Certain basicadvantages of the screw-type devices however are so desirable that theyhave been accepted, to a considerable degree, despite their knowninadequacies.

To produce a more ideal blower of this type, it is necessary that thesealing line between the rotors remain unbroken as the rotors revolve,that the rotors and associated shafts be of rigid design, that therotors be of such shape that they can be made accurately andeconomically, that no sealed pockets are formed, and no leakage openingsdevelop as the rotors revolve. All these desirable objects may beaccomplished with the new rotors as disclosed herein. I

The number of threads on each rotor is generally a matter of choice anddepends upon the speed, pressure and other considerations. A largernumber of threads is generally chosen for extremely high speed and highinternal compression ratio. The other extreme would be two threads onthe main rotor and three or four on the gate rotor. Any of thesecombinations will operate and all will have certain advantages overother combinations. However, it is believed three threads on the mainrotor and four threads on the gate rotor provide the ,best and mostuniversal combination and this disclosure Will be directed to such acombination but is not limited thereto.

When accurately formed, complementary threads of the rotor members willoperate as smoothly as a set of gears and the main rotor can be used todrive the gate rotor. However, in actual use the rotors usually operatewithout lubrication on the thread surfaces and also, because of the highspeeds at which these devices operate, it is generally advisable toprovide timing gears, and rotors with certain fixed clearances, so thatthe rotors operate in timed relation and do not contact each other orthe housing. It has been found that should the rotors contact eachother, or the housing, the friction between the parts will produce heatand cause failure. Thus, it is important to have rigid parts that canabsorb considerable power without deflecting and making contact withother parts. Furthermore, as the rotors do not make contact with eachother or with the housing they are not subject to wear. Thus, thisimproved device has two fundamental desirable features. The rotors donot require lubrication and are not subject to wear.

The principal object of this invention is to provide rotors havingmultiple arc generation in combination with directed diagonal dischargeair flow.

A second important object of this invention is to eliminate the sealedpockets formed at the discharge end just before the pockets run out.

Another object is to provide wide, unbroken, highly effective sealinglines.

Another object is to provide rotors that form pockets which run out tozero without loss in capacity.

Another object is to provide a device in which both rotors can beeffectively cooled by liquid circulated therein.

Another object is to provide a gate rotor having threads that are wellsupported against deflection.

Another object is to provide a gate rotor that will accommodate a largershaft than heretofore possible without reducing the capacity of thedevice.

Another object is to provide the main rotor with a tapered end which isnon-uniform in cross-section, and a complementary, tapered re-entrantring on the housing end wall to form a seal therewith.

Another important object is to provide such a device that is suitablefor higher speeds and pressures.

Another object is to provide a blower wherein the rotor and includingthe nomenclature terior.

axes of the rotor members on line A-A of Fig. 2. "Fig. 2 is alongitudinal sectional view taken through the axis of the main rotor online B-B of Fig. l, at a right angle to the view in Fig. l, and showingthe suction and discharge ports.

' Fig. 3 is a perspective view of a pair of rotors per se embodying theinvention.

Fig. 4 is a plan view of a pair of mating rotors, in

mesh, having more than normal length and especially adaptable for highpressure.

Fig. 5 is a sectional view taken on the line H--H of Fig. 48 through theuniform end section of the main rotor and including the nomenclature ofthe rotor exterior.

- Fig. 6 is a sectional view taken on the line H-H of Fig. 48 throughthe uniform end section of the gate rotor and including the nomenclatureof the rotor exterior.

Fig. 7 is a sectional view taken on the line F-F of Fig. '48 through thenon-uniform end section of the main Fig. 8 is a sectional view taken onthe line F--F of gate rotor and including the nomenclature of the rotorexterior.

. Fig. 9 shows the development of the generated thread surfaces on themain rotor by the describing arcs on the gate rotor.

, Fig. 10 is a perspective view of a pair of conventional rotors in fullmesh showing the formation of the sealed pocket at the discharge endthereof.

' Fig. 11 diagrammatically shows a main rotor being described, orgenerated, by the crest edge of the gate rotor, ,providing single arcgeneration and line scaling in accordance with the invention, a tip ofthe gate rotor being shown in three different positions relative to themain rotor.

- 'Fig. 12 diagrammatically shows a main rotor being described, orgenerated, by the crest edge and intersection protuberance of the gaterotor providing multiple arc generation and band scaling in accordancewith the invention, a tip of the gate rotor being shown in threedifferent positions relative to the main rotor.

Fig. 13 diagrammatically shows multiple arc generation .on the gaterotor by multiple describing arcs on the main rotor, a thread of themain rotor being shown in three different positions relative todifferent threads of the gate rotor.

" Fig. 14 diagrammatically shows single arc generation ,on the gaterotor by the crest edge of the main rotor, a thread of the main rotorbeing shown in three different positions relative to different threadsof the gate rotor. Fig. 15 diagrammatically shows the difference betweensingle and multiple arc generation on a main rotor thread incross-section.

M Fig. 16 diagrammatically shows the difference between single andmultiple arc generation on a gate rotor thread in cross-section.

' Fig. 17 is a side elevation showing the continuous seal line on a mainrotor having multiple arc generation.

Fig. 18 is a side elevation showing the complementary seal line on agate rotor having multiple arc generation. Fig. 19 is a longitudinalsectional view showing a single they approach the center of the rotorexare generation line seal on the side of a main rotor '4 point betweenthe main and gate generation.

Fig. 21 is a longitudinal sectional view showing a multiple arcgeneration band seal on the side of a main rotor thread, the rotor beingshown untwisted for clarity.

Fig. 22 is an end view showing the band sealing contact between the mainand gaterotors with multiple arc generation.

Fig. 23 is a longitudinal sectional view showing a single arc generationline seal on the gate rotor thread, the rotor being shown untwisted forclarity.

Fig. 24 is an end view showing the crest edge of the main rotorproducing the line seal on the gate rotor.

Fig. 25 is a longitudinal sectional view showing a multiple arcgeneration band seal on one side of the gate rotor thread, the rotorbeing shown untwisted for clarity.

Fig. 26 is an end view showing the area of congruency between the mainand gate rotors which produces the band seal line.

Fig. 27 is a fragmentary portion of a main rotor showing the rotorthread on which the non-uniform end is tapered to provide a land at thetip having uniform. width throughout the length of the rotor. I

Figs. 28 to 33 inclusive are transverse vertical sectional views througha housing and rotors showing rotors having multiple arc generation invarious positions of engagement as later described in detail.

Figs. 34 to 36 inclusive are vertical end views respective ly showingdifierent corresponding positions of the cutting position ofthemachining tools and the main rotor relative to the gate rotor, whenproducing multiple arc generation.

Fig. 37 is an endview showing the position of the cutting tools inrelation to the finished main rotor for multiple arc generation of thegate rotor.

Fig. 38 is an end view showing single arc, or single point, generationof the gate rotor.

Fig. 39 is an end view showing an alternative method of machining thecongruent tip portion of the gate rotor, this being a separate operationpreferably made after the rotor has been generated.

Figs. 40 to 42 inclusive are end views showing respectivelydifierentcorrmponding positions of the machining tools and gate rotorrelative to the main rotor when producing multiple arc generation.

Fig. 43 is a side view of the cutting tool holder for form ing the mainrotor.-

Fig. 44 is a longitudinal sectional view showing a machined gate rotorbored out at one end in the form of a taper, the ends of the threads notshown projected in the tapered bore and the rotor being untwisted forclarity, the section being taken on the line V--V of Fig. 42.

rotors with single arc ,Fig. 45, is a longitudinal sectional view of afinishedcone ready to be fixedly attached within the tapered bore of thegate rotor.

Fig. 46 is a vertical end view of the cone shown in Fig. 45 as viewedfrom the largest end.

Fig. 47 is a transverse sectional view showing a section through thenon-uniform end section of the gate rotor after the cone shown in Figs.45-46 is welded in place, the section being taken on the line F-F ofFig. 48.

Fig. 48 is a fragmentary longitudinal sectional view through thenon-uniformed end section of the main and gate rotors in meshedposition, the rotors having multiple are generation and shown untwistedfor clarity, the section being taken on the line D--D of Fig. 49.

Fig, 49 is an end view of the uniform end section of the rotors.

Fig. 50 is an end view of the non-uniform end section of the rotors.

Figs. 51 to 53 inclusive are sectional views taken through thenon-uniformed end section of the rotors as seen respectively on thelines E-E, F-F, and 6-6 of Fi 48- f Fig. 54 diagrammatically shows thedevelopment. of the non-uniform end of the main rotor.

F1g. 55 is a side view of the blower housing partially In section.

Fig. 56 is an end view of the housing, partially in sectron on the lineK-K of Fig. 55, looking into the open end thereof against the integralsuction end wall.

Fig. 57 is a sectional view of the housing taken on line C-C of Fig. 2and looking against the removable end wall thereof.

Fig. 58 is a plan view of the inner face of the discharge end wall andshowing the tapered ring section in place.

Fig. 59 is a vertical section of the discharge end wall taken on theline J] of Fig. 58.

Fig. 60 is a horizontal sectional view of the end wall taken on the lineII of Fig. 58.

Fig. 61 is a vertical sectional view of the re-entrant centering plateshown detached from the end wall.

Figs. 62 to 64 are vertical sectional views and showing the dischargeport outline as used with generated rotors uniform throughout the lengththereof, the various positions of the rotors being shown in phantom. Inthese Figs. 62-64 it is intended to show the rotor positions and notsections of the rotors themselves.

Fig. 65 is a fragmentary longitudinal sectional view on the line LL ofFig. 66 and showing the non-uniform ends of a pair of alternate rotorforms, the rotors being shown untwisted for clarity.

Fig. 66 is an end view of the opposite or uniform end section of therotors shown in Fig. 65.

Fig. 67 is an end view of the non-uniform end section of the rotorsshown in Fig. 65.

Figs. 68 to 70 are transverse sectional views of the rotors takenrespectively on lines M-M, N-N and OO of Fig. 65

Fig. 71 is a longitudinal sectional view of the power circuit as appliedto blowers.

Fig. 72 is a fragmentary end view of the rotors illustrated withexaggerated clearance between the rotor threads.

Fig. 73 is an end view showing the intersections of the curves on themain rotor threads rounded to provide multiple arc generation on themain rotor and to describe multiple arc generation on the gate rotor asshown in Fig. 74.

Fig. 74 is an end view showing the intersections of the curves on thegate rotor threads rounded to provide multiple arc generation on thegate rotor and describing multiple arc generation on the main rotor asshown in Fig. 73.

Fig. 75 is an end view showing the intersections of the curves on themain rotor thread not rounded and providing multiple point generation onthe main rotor and describing multiple point generation on the gaterotor as shown in Fig. 76.

Fig. 76 is an end view showing the intersections of the curves on thegate rotor thread not rounded and providing multiple point generation onthe gate rotor and describing multiple point generation on the mainrotor shown in Fig. 75.

Fig. 77 is a longitudinal sectional view of a blower of which thehousing, discharge end wall, and both rotors are arranged to be liquidcooled.

Fig. 78 is a longitudinal sectional view illustrating an alternatemethod of cooling the rotors.

Fig. 79 is a plan view of a pair of rotors in mesh, the rotors havingmultiple arc generation and being uniform throughout their length.

Fig. 80 is a transverse sectional view of the housing showing anotherembodiment of discharge end wall dif fering from that shownin Fig. 57.

Fig. 81 is a fragmentary longitudinal section of the blower showing athrust balancing pocket.

Fig. 82 is a fragmentary end view showing the band sealing zone locatednear the tip of the main rotor thread.

Fig. 83. is a view similar to Fig. 82 but showing the band sealing zonelocated, at the root of the main rotor thread.

Fig. 84 is another view similar to Fig. 82 but showing the gate rotorlarger in diameter than its pitch circle.

Fig. 85 is an end view of fragmentary portions of rotors havingasymmetrical thread profiles.

Fig. 86 is a fragmentary longitudinal sectional section of the dischargeend of the rotors embodying an alternate design of cone on the gaterotor which is larger than the outside diameter of the rotor, the rotorsbeing shown untwisted for clarity.

Fig. 87 is a view similar to Fig. 86 but showing both of the rotorshaving a short cylindrical end on the nonuniform end of the rotors, therotors also being shown untwisted for clarity.

Figs. 88 to 101 inclusive are longitudinal sectional views showingalternative forms for the gate rotor, the rotors being shown untwistedfor clarity.

In the specification and claims certain terms such as pockets, run-out,timing and timing gears are used and to render the meaning thereofclear, the following definitions are set forth:

Pockets-The spaces or cavities formed by the coaction of the rotorthreads in conjunction with the housing chamber walls. These pockets areactually the spaces that are filled with the fluid being pumped. Duringop"- eration of the device the pockets form continuously at the suctionend of the rotors and vanish continuously at the discharge end of therotors.

Run-out.This term is generally applied in connection with the pockets asthey reach the discharge end and decrease in size to zero, or vanish.The pockets form at the suction end and increase to maximum size as therotors rotate. These pockets continue to fill with the fluid beingpumped until they reach maximum size. They are then disconnected fromthe suction port by the rotor thread action relative to the suction portedges and the pockets then begin to decrease in size and compress thefluid contained therein. Compression continues until the pocketregisters with the discharge port and discharge of the fluid takesplace. The pocket continues to decrease in size until it completelyvanishes, or runsout at the extreme end of the rotors.

Timing gears.-Gears used to time the rotors and keep them in timedrelation to eliminate contact between the threads of the mating rotorswhen the device is in operation. The clearance between the gear teethmust be less thanv the clearance between the rotor threads if contact isto be avoided. For example, the clearance, or backlash, between thetiming gears usually is within the range of .002" to .003", while theclearance between the rotor threads may be within the range of .020" to.040", and depends upon the size of the device. Thus the rotor threadscan not contact each other as they are held in timed, or spaced,relation by the timing gears.

Timing.Timing is the act of setting, or locating, the timing gearsrelative to the rotors so that the main rotor threads may pass throughthe troughs of the gate rotor without making contact as indicated inFig. 72. As shown in Fig. 71, the gate rotor timing gear 52 is usuallymade separately from its hub 53 and is adjustable therewith tofacilitate the timing operation. This timing operation is explained indetail in Whitfield Patent No. 2,683,994.

Referring to Figs. 1 and 2, the housing 10 of the pump contains twoparallel cylindrical chambers 12 and 14 disposed side by side inparallelism and merging into one another, forming a common chamber, thecrosssection of which is somewhat in the form of a figure 8. One end ofthe housing is provided with an integralend wall 16 which forms one endwall of the chambers 12 and 14. The other end of the housing is providedwith a removable end wall 18 which is centered in the rotor chambers bythe. re-entrant. internally tapered exten-v '7 sion ring 20 and thecentering plate 22. The centering 'plate 22 is centered in the housingchamber by its outside diameter and is centered on the end wall 18 bythe cylindrical projection 24.

The head 18 is provided with circular openings 26 and 28, opening 26being provided with a bearing bushing 39 for the main rotor shaft 32 andthe opening 28 receives the projection 24 on the centering plate 22. Thecentering plate is provided with a bearing bushing 34 for the gate rotorshaft 36. The integral end wall 16 is also provided with openings 38 and40 which are provided with hearing bushings 42 and 44 respectively. Mainrotor 46 is fixedly attached to the shaft 32 and the gate rotor 48 isfixedly attached to the shaft 36, the retors revolving in theirrespective chambers and being maintained in timed relation by the timinggears 50 and 52 fixedly attached on the main rotor shaft 32 and gaterotor shaft 36 respectively.

Referring to the drawings, the motor employed to il- A portion 144 ofthe end wall 16 is offset from the remainder of the wall to form oneside of the suction port 54, the exact shape of the suction port beingdescribed later. Diagonally opposite the suction port 54 is thedischarge port 56 which also may have one side wall offset and recessedinto the end wall 18, also described in detail later. The open end ofthe housing is so formed that the intersecting chambers 12 and 14 form asupport to locate and properly center the end wall 18 with chambers 12and 14, the re-entrant ring 20 and the centering plate 22 fitting withinthe ends of said chambers. Since the shaft openings 38 and 40 in theintegral end wall 16 are machined centrally with the rotor chambers 12and 14 respectively, the central location of the rotors is assured andthey may operate in their chambers with very small clearance withoutliability of contacting the housing. The re-entrant ring 20 and thecentering plate 22, while fitting neatly with their respective chambers12 and 14, are slightly larger in diameter than the respective rotors 46and 48 to provide a fixed running clearance between the rotors andchamber walls. Various methods of controlling the thrust of the rotorsare applicable and well known in the art and therefore special thrustmeans are not shown or claimed. However, it will be understood thatsuitable thrust means will be employed.

The rotor members which are mounted within the housing chambers comprisemating helical screw thread members 46 and 48 which are arranged tooperate within the intersecting cylindrical chambers 12 and 14respectively. For convenience the member 46 is termed the main rotor andthe member 48 is termed the gate rotor. Power may be applied to therotors to force fluid from the suction port to the discharge portagainst pressure, or fluid may be supplied to the device under pressureand the device then will act as a motor to supply rotative power.

The main rotor 46, as shown, is provided with three circumferentiallyevenly spaced helical threads 58, 58 and 58 of identical contour, thedetails of which are later described. The rotor 46 preferably operateswithin its chamber without making contact with the housing, the endwalls, or the other rotor. As an altcrnatitve it could have only twothreads or more than three threads, if desired.

, The gate rotor 48, as shown, is provided with four circumferentiallyevenly spaced helical threads 64, 64, 64", and 64 which are formed so asto be complementary to the main rotor threads and the gate rotor alsopreferably operates without contacting the housing or the main rotor.Likewise, as an alternative, the gate rotor could have more or less thanfour threads, if desired, but the ratio of three main rotor threads andfour gate rotor threads is preferred.

After the rotors are assembled within the housing the gears 50 and 52are properly located on the respective shafts 32 and36 to correctly timetherotors. That is,

8 the timing gears must he s'olocated relative to the rotor threadsthat, as the rotors revolve, the rotor threads will be restrained by thetiming gears from contacting each other. This will be described later indetail as it is an important part of this invention.

In describing the details of the rotors that form the principal objectof this invention, reference is made especially to Figs. 3, 5, 6, 7, 8and 9. Other references will follow as the description progresses.

In Figs. 1 through 4, the main rotor 46 is shown with the ends of thethreads cut away from the land at the tip 72 to the land at the root 74in a tapered manner thus forming a rotor having a uniform end sectionand a nonuniform end section. In the uniform end section thecross-sectional shape does not change; while in the nonuniform endsection the cross-sectional shape changes continuously, generallytapering toward the end. The sides of the threads are generated, ordescribed, throughout their length, by the gate rotor. The outer portion76 of the thread surface is generated by the intersection protuberance78 of the gate rotor, the root portion 80 is generated by the crest edge82 of the gate rotor, and the congruent band seal zone 84 is formed bythe intersection of the generated curves 76 and 80. The generated outerportion 76, the congruent band seal zone 84, and the generated rootportion 80 extend entirely across the uniform rotor end section andcontinue across the non-uniform rotor end section, ending at the crestedges 104 of the tapered portion of the threads in the non-uniform endsection.

Another description of the nature of the main rotor would be to state arotor is made with a uniform crosssection throughout its length, usingany desired crosssectional form, and then one end or corner of eachthread is cut away to form the non-uniform end section. The threads arepreferably cut away in a conical manner as shown, the tapered tip landsurface forming an angle of about 30 in relation to the shaft center. Ofcourse the tapered surface need not form a straight line but can be madein any form to easily seal with the gate rotor and housing, or gaterotor and end wall. The cutting angle also need not be 30 but can bemade as desired. However, the preferred form is shown.

It appears that the removal of the corners of the main rotor threads andthe addition of the cone to the gate rotor may appear to reduce thecapacity of the device. However, this is not necessarily true as blowerswith this feature can be operated at higher speed and also, since thecone in the gate rotor provides for a larger shaft and support for thethreads, the troughs in the gate rotor may be made deeper in the uniformend section of such rotors. Thus the advantages of the invention can beutilized without a loss in capacity.

Other suggested forms for cutting away the main rotor threads would becomplementary to the gate rotor forms shown in Figs. 88 to 101inclusive. The point of intersection 84 of the two curves 76 and 80 maybe reduced slightly, if necessary, to better form a congruent seal withthe band seal Zone 86 on the gate rotor but it has been found that thetwo curves 76 and 80 form a very nearly smooth meeting under usualconditions and further smoothing may not be necessary or desirable asthis same intersection point 84- describes the band seal zone 86 on thegate rotor.

The land 74 at the root of the threads is a helical surface uniform inwidth and diameter throughout the length of the rotor and forms arolling seal with the land 88 on the tip of the gate rotor which islikewise uniform in width and diameter throughout the length of therotor. The land 72 at the tip of the thread of the main rotor is uniformthroughout the uniform section of the rotor and forms a. seal with thewall of the chamber 12 in the housing 10. The land at the tip of thethread in the non-uniform end section of the main rotor is non-uniform,widening toward the end of the rotor as its diameter de-

